S253: IMPAIRED HSC FITNESS AND ACCELERATED LEUKEMOGENESIS IN A MOUSE MODEL OF CHRONIC INFLAMMATION
Authors: Srdjan Grusanovic, Monika Burocziova, Petr Danek, Maria Kuzmina, Miroslava Kari Adamcova, Romana Mikyskova, Karolina Vanickova, Sladjana Kosanovic, Jana Pokorna, Milan Reinis, Tomas Brdicka, Meritxell Alberich-Jorda
Journal: HemaSphere (2023)

Background: Chronic inflammation (CI) is a hallmark of autoinflammatory disorders and is characterized by excessive production of cytokines. CI has been proposed as a factor that promotes solid tumor progression and metastasis. Accordingly, population-based studies identified a history of CI diseases as a risk factor for leukemia development. In order to investigate how CI affects hematopoietic stem cells (HSCs), as well as how it promotes leukemia development, we employed a mouse model suffering from chronic multifocal osteomyelitis (CMO). CMO mice exhibit a progressive autoinflammatory disorder that resembles human chronic recurrent multifocal osteomyelitis. CMO mice are asymptomatic until 7 weeks old, and after develop swollen paws, tail kinks, increased bone marrow (BM) cellularity, number of granulocytes, and production of cytokines. Aims: To investigate (1) how sterile CI affects HSCs, (2) identify the mechanisms that are mediating these effects, and (3) determine whether the inflammatory environment can accelerate AML development. Methods: Flow cytometry, generation of murine chimeras, limiting dilution transplantation assays, competitive BM transplantations, RNA sequencing, intraperitoneal injection of IL-6-, IL-6R-blocking antibody or Stat3 inhibitor, phospho-flow analysis, survival assays, MLL-AF9 retroviral infection, TP53 deficient mouse model Results: Our data showed that CMO HSCs are expanded in asymptomatic mice, and that this expansion continued as the mice grew older. Limiting dilution transplantation assays indicated that CMO HSCs are functionally impaired. Interestingly, MyD88-deficient CMO mice did not develop the inflammatory phenotype, however their HSC population was still expanded and functionally impaired. Next, we generated chimeras to investigate the effect of the CMO immune compartment and the CMO BM niche on HSCs. Our results showed that both CMO compartments affect HSC functionality. Furthermore, RNAseq analysis suggested that the loss of HSC function is in part mediated by the IL-6/Jak/Stat3 signaling pathway. Indeed, we detected increased levels of IL-6 in CMO serum, BM, as well as increased pStat3 levels in CMO HSCs. Treatment of CMO mice with IL-6- or IL-6R-blocking antibody significantly prevented the HSC expansion, while targeting pStat3 prevented their expansion and functional impairment. Remarkably, MLL-AF9 leukemic cells demonstrated a faster leukemic onset in CMO mice than in WT mice, and they exhibited enhanced growth in vitro when IL-6 was added to the cultures. Next, we investigated whether CI promotes cancer progression in a TP53 deficient mouse model. We crossed CMO mice to TP53-deficient mice, and monitored their survival. Remarkably, CMO/Tp53+/- double mutants showed significantly accelerated tumor development and succumbed to disease faster than Tp53+/- non-inflammatory mice. TP53 deficient mice do not exhibit myeloid transformation, however, we observed AML development in one CMO/Tp53+/- mouse, suggesting that CI might induce AML transformation in some genetically predisposed murine models. Summary/Conclusion: Altogether, our data indicate that CI has a detrimental effect on HSCs and highlight the possibility of adding clinically available Stat3 inhibitors to the current treatment in order to preserve stem cell functions. Further, our results suggest that CI acts as an additional factor in the development of AML, providing additional understanding of the mechanisms of transformation. The work was partially funded by the National Institute for Cancer Research (Program EXCELES, ID Project No. LX22NPO5102)-Funded by the European Union-Next Generation EU. Keywords: Inflammation, MLL, STAT3, Bone marrow niche